Plants are constantly exposed to a variety of biotic (i.e. pathogen infection and insect herbivory) and abiotic (i.e. high or low temperature, drought, flood and salinity) stresses. To survive these challenges to their sessile life, plants have developed elaborate mechanisms to perceive external signals and to manifest adaptive responses with proper physiological and morphological changes (Bohnert et al. 1995). Plants exposed to cold or chilling conditions typically have low yields of biomass, seeds, fruit and other edible products. The term “chilling sensitivity” is used for the description of physiological and developmental damages in the plant caused by low, but above freezing, temperatures. Important agricultural crop plants such as corn, soybean, rice and cotton have tropical ancestors that make them chilling sensitive. In some countries or agricultural regions of the world chilling temperatures are a significant cause of crop losses and a primary factor limiting the geographical range and growing season of many crop species. Another example is that chilling conditions can cause significant concern in early spring planting of corn or canola. Poor germination and reduced growth of chilling sensitive crops in the spring results in less ground coverage, more erosion and increased occurrence of weeds leading to less nutrient supply for the crop.
Typically, chilling damage includes wilting, necrosis or ion leakage from cell membranes, especially calcium leakage, and decreased membrane fluidity, which consequently impacts membrane dependent processes such as: photosynthesis, protein synthesis, ATPase activity, uptake of nitrogen, etc. (see Levitt J (1980) Chilling injury and resistance. In Chilling, Freezing, and High Temperature Stresses: Responses of Plant to Environmental Stresses, Vol 1., T T Kozlowsky, ed, Academic Press, New York, pp 23-64; Graham and Patterson (1982) Annu Rev Plant Physiol 33: 347-372; Guy (1990) Annu Rev Plant Physiol Plant Mol Biol 41: 187-223; and Nishida and Murata (1996) Annu Rev Plant Physiol Plant Mol Biol 47: 541-568.). In addition, cold temperatures are often associated with wet conditions. The combination of cold and wet can result in hypoxic stress on the roots, causing an even more severe reduction of growth rate but, more critically, can be lethal to the plants, especially sensitive plant species such as corn and cotton.
Yet it has been observed that environmental factors, such as low temperature, can serve as triggers to induce cold acclimation processes allowing plants responding thereto to survive and thrive in low temperature environments. It would, therefore, be of great interest and importance to be able to identify genes that regulate or confer improved cold acclimation characteristics to enable one to create transformed plants (such as crop plants) with improved cold tolerance characteristics such as faster germination and/or growth and/or improved nitrogen uptake under cold conditions to improve survival or performance under low or chilling temperatures.
In the fields of agriculture and forestry efforts are constantly being made to produce plants with an increased growth potential in order to feed the ever-increasing world population and to guarantee the supply of reproducible raw materials. This is done conventionally through plant breeding. The breeding process is, however, both time-consuming and labor-intensive. Furthermore, appropriate breeding programs must be performed for each relevant plant species.
Progress has been made in part by the genetic manipulation of plants; that is by introducing and expressing recombinant nucleic acid molecules in plants. Such approaches have the advantage of not usually being limited to one plant species, but instead being transferable among plant species. There is a need for generally applicable processes that improve forest or agricultural plant growth potential. Therefore, the present invention relates to a process for increasing the growth potential in plants under low temperature, chilling or cold conditions, characterized by expression of recombinant DNA molecules stably integrated into the plant genome.